Whew! You really touched me deeply with this story. I was completely drawn in, but part of my mind kept begging, "No, please, Snape isn't Snape without his memories, without his past." So the "Mr. Potter" line (right after hot smut that totally took my breath away) was just what I wanted to see.
When one remembers how Snape fooled Voldie, it's easy to imagine that he could adopt an entirely new persona and pretend to have no memories at all even after months of conversation.
My favorite part (well, possibly after the sex) was Snape's predictions for the future. That's absolutely spot on what I was desperately hoping for. It actually brought tears to my eyes.
In retrospect, I adore what Harry told Snape about the war, and that Severus was able to continue the charade even though those had to be words he had needed to hear for so long.